Electrosurgery is the use of an electric current to effect tissues in surgical procedures. Electrosurgery can be practiced using bipolar or monopolar modality. In a bipolar mode, electrosurgical equipment passes current between two conductive parts of the instrument, resulting in an arc. Tissue positioned between the conductive parts is vaporized and the wound site is cauterized by the heat generated in the electrical discharge. In monopolar modality, the patient is incorporated into an electric circuit, such that the patient supplies a ground contact to an instrument that is in ohmic contact with a high energy electron source (the electrosurgical generator). Discharge between the electrosurgical instrument and the patient produces the electrosurgical effect.
The basic procedures available using monopolar electrosurgical equipment are cutting, fulguration, desiccation, and coagulation. Cutting occurs when a surgeon selects voltage and current settings such that cells in the subject tissues are vaporized. Because of the heat involved, electrosurgical cuts are usually accompanied by hemostatis in the surgical wound, however, it is possible to select power settings in which a purely surgical cut is effected by an electrosurgical scalpel.
Fulguration, a combination of tissue dehydration and charring, occurs at high voltage settings and is used generally to seal tissue over a wide area. To reduce tissue destruction, fulguration is generally preformed with a modulated power source, such that the power is only applied to the electrosurgical device in short “bursts”. The power can be adjusted to give a range of effects which yield a wound ranging from dehydrated tissue covered with a light eschar to tissues layered in charred material over eschar over dehydrated tissues. Cutting and fulguration are accomplished by discharge from the electrode to the tissue (no tissue contact with the electrode).
Desiccation is accomplished by directly contacting cellular tissue with a low voltage electrosurgical current. This direct contact generates sufficient heat to dehydrate the upper layer of cells (desiccation) but does not generate sufficient heat to vaporize or rupture the cellular structure.
The quality of the wound produced by electrosurgical devices, thus the degree to which hemostatis can be achieved and the level of trauma imparted to tissues during the procedure, and subsequently, the ease of healing of the surgical wound after the procedure can be controlled by tailoring the quality of the electrosurgical discharge during the procedure. One method of moderating the destructive effects of electrical discharge has been accomplished through the introduction of a gas stream into the discharge path of an electrosurgical apparatus. In gas enhanced electrosurgery, an inert gas which is easily ionized, such as argon or helium, is introduced into the surgical site. The gas is used both to moderate the discharge, making for a more uniform arc to the surgical site, and to “blanket” the surgical site, such that charring (burning) of the tissue is suppressed. It is thought that easily ionizable gasses also reduce heating of the electrode, and thus suppress electrode destruction and material transfer from the electrode to the tissue.
Thus, U.S. Pat. No. 2,618,267 to Hanriot discloses a control system for controlling a gas blanket directed at blanketing an electrosurgical instrument. This patent does not teach management of the gas stream regarding contact of the instrument with the surgical site.
U.S. Pat. Nos. 2,708,933 and 2,828,747 to August disclose electrosurgical instruments utilizing an argon shroud about the cutting element of the instrument, the purpose of which is to prevent contacting explosive anesthesia vapors with electrical discharge. These patents do not teach the management of inert gas pressure during contact of the instrument with tissues in the surgical site.
In U.S. Pat. No. 4,040,426 to Morrison, an electrosurgical device is described in which argon or helium is flowed through a tube arranged coaxially about an electrode that protrudes from the end of said tube. The '426 patent teaches that electrostatic charge is built up on the surrounding tube by the flow of gas through the tube, which participates in corona discharge between the electrode and the surrounding tube. This discharge produces a stream of ionized gas that participates in facilitating discharge between the tissue at the surgical site and an electrode (when this assembly is employed in an electrosurgical device) without contact between the tissue and the electrode. The '426 patent teaches that discharge occurs along the length of the coaxial tube that is proximate to the electrode while gas is flowing and the electrode is energized. The '426 patent teaches that the arrangement disclosed dissipates power from an electrosurgical generator along the gas tube/electrode pathway rather than through the electrode/tissue gap of conventional electrosurgical arrangements.
U.S. Pat. No. 4,060,088 to Morrison et al. teaches the use of a hollow electrode in an electrosurgical apparatus, wherein an inert gas is passed through the electrode, providing a low resistance discharge pathway to the surgical site. Additionally, the '088 patent teaches the use of a hollow electrode coaxially placed within a gas conduit. In such an arrangement, a columnated beam of ionized gas can be directed at a surgical site when such a construct is employed in an electrosurgical apparatus. Such a beam was disclosed to be effective in controlled fulguration procedures leading to superior condition of the tissues in the surgical site over electrosurgical fulguration methods not employing an inert gas in the electrical discharge. The '088 patent teaches that there is no functional difference between an electrode protruding from the jacket conducting gas past the electrode and one contained wholly within such a jacket in the effectiveness of the device in fulguration procedures.
U.S. Pat. No. 4,781,175 to McGreevy et al. discloses an electrosurgical apparatus consisting of a pencil unit which embodies an electrosurgical instrument, a gas delivery unit, and an electric power delivery unit. The '175 teaches, with regard to electrical discharge from the electrosurgical instrument, that a gas jet can be interfaced with the electrosurgical instrument which will facilitate a more even and stable discharge between the apparatus and the surgical wound and clear fluids from the surgical site during cutting procedures. The '175 patent discloses a surgical pencil for carrying out surgical procedures having an inert gas dispensing nozzle, and in which the electrode of the device is contained within that nozzle. No teaching is imparted regarding the shape or material of the electrode used in the disclosed electrosurgical pencil.
U.S. Pat. No. 4,927,420 to Newkirk et al. discloses how to make and use a refractory alloy electrode in an electrosurgical instrument. The disclosed refractory metal electrode is characterized by its resistance to thermal degradation of its finely formed end. The '420 patent discloses that by fitting electrosurgical instruments with electrodes having tips of small cross-sectional area, tissue damage common with instruments employing large cross-sectional area electrodes is reduced. The '420 patent also teaches how to make electrodes with the subject small cross-sectional area tip from refractory metal wire. The '420 patent discloses that the subject electrodes may be employed with mono- or bipolar electrosurgical systems, but does not teach or disclose use of the electrodes with inert gas blanketing
U.S. Pat. No. 5,098,430 to Fleenor discloses an electrosurgical pencil that has a retractable nozzle enclosing an electrode which is retractable at the surgeons will during a procedure. Using this device, an electrosurgical implement can be operated in both gas enhanced non-contact mode or non-gas enhanced direct contact mode. The '430 patent teaches that in ordinary equipment, the instrument arrangement required for gas enhanced fulguration is not compatible with that required in an instrument intended for direct contact electrosurgical dissection. The requirements for a laminar flow shield completely isolating the electrode of the instrument precludes using such an implement because the electrode can not be contacted to the tissue when shielded for gas enhanced operation. The '430 patent discloses and instrument that can be used in conventional (non-gas enhanced) direct contact electrosurgical procedures such as cutting, and in gas enhanced (non-contact) fulguration of tissues, permitting a surgeon to engage in a full range of electosurgical techniques with one implement. The '430 patent additionally discloses a control mechanism mounted on the surgical pencil affording a surgeon operation of the electrosurgical apparatus and the retractable nozzle using the same hand controlling the pencil during a surgical procedure.
Although prior art has taught a number of methods by which electrosurgical discharge may be utilized in delicate surgical work, and has taught gas enhancement of tissue fulguration as a method of improving surgical result, some problems still remain. In general electrosurgical procedures, contact with tissue usually results in tissue adhering to the electrode. The adhered tissue can rip open the surgical wound, complicating the outcome of the surgery. To counteract this tendency, fully coated prior art electrodes have been produced, however these devices require higher voltages to overcome the impedance and resistance offered by the coatings. These higher voltages can exacerbate discharge instability, concentrating the energy of the electrosurgical instrument in very localized areas. This concentrated discharge leads to uneven eschar and often to excessive tissue necrosis in the surgical wound. In endoscopic procedures, electrode insulation can serve to facilitate the formation of an unintended capacitance in the electrosurgical instrument which discharges in an unintended manner through the patient which can result in unintended tissue damage.
In a gas enhanced mode, accidental contact of the electrosurgical instrument with the tissues in the surgical site can lead to the formation of a gas embolism in the patient, which can lead to surgical complication or death of the patient. The present invention addresses these problems associated with gas enhanced, monopolar electrosurgical instruments.